1. Technical Field
The present invention relates to a positioning method, a computer program, a positioning device, and an electronic apparatus.
2. Related Art
As a positioning system that makes use of artificial satellites, a GPS (Global Positioning System) is widely known. The GPS is used in positioning devices incorporated in a portable phone, a car navigation apparatus, and the like. In the GPS, a positioning device measures the present location of the device by performing positioning calculation for calculating values of four parameters, i.e., coordinate values of three dimensions indicating the location and the clock error of the device, on the basis of information such as locations of plural GPS satellites and pseudo distances from the respective GPS satellites to the device.
However, in the positioning performed by using satellite signals from positioning satellites, there are various error factors such as the influence caused by a so-called multi-path and it is difficult to prevent occurrence of positioning errors. Therefore, various techniques for reducing the positioning errors are devised. As an example of the techniques, JP-A-2001-337156 discloses a technique concerning positioning processing employing a Kalman filter.
The technique disclosed in JP-A-2001-337156 is a technique for comparing the velocity of a positioning device and a threshold of velocity set in advance to thereby judge whether the positioning device remains stationary and changing parameters of the Kalman filter on the basis of a result of the judgment. However, since the threshold of velocity is set as a fixed value, it is likely that an accurate positioned location (a location subjected to filtering by the Kalman filter) is not calculated unless a moving state of the positioning device is properly judged.
As a specific example, when a user carrying the positioning device is walking, in some case, the measured velocity of the positioning device does not meet the threshold and the positioning device is judged as remaining stationary regardless of the fact that the positioning device is actually moving. In this case, a parameter for judging that the positioning device is in a stationary state is set in the parameters of the Kalman filter. As a result, the Kalman filter acts to suppress fluctuation in the positioned location. Therefore, a location delay occurs in the positioned location with respect to an actual location of the positioning device and follow-up ability of the positioned location falls.
When the user carrying the positioning device is driving a car, in some case, even in a state in which the car is stopped, the velocity of the positioning device is not correctly measured if a reception environment of satellite signals is dissatisfactory and, regardless of the fact that the positioning device actually remains stationary, the positioning device is misjudged as moving. In this case, a parameter for judging that the positioning device is in a moving state is set in the parameters of the Kalman filter. As a result, since the Kalman filter acts to facilitate fluctuation in a positioned location, it is likely that a location far apart from an actual location of the positioning device is outputted.